肠道微生物与猪代谢特征的关系及对话机制

To improve meat quality is a major issue facing the current pig industry. Host metabolic status plays a causal role in determining pork quality. Gut microbiota, our second genome, which is closely related to host metabolism, physiology and the presence of obesity and relevant diseases. It is not clear whether gut microbiota mediated the metabolic distinction between Chinese indigenous pigs and imported pigs. Short chain fatty acids (SCFAs) act as a link between gut microbiota and host’s metabolism, and adenosine monophosphate-activated protein kinase (AMPK) is a critical molecular in regulating cell metabolism. SCFAs are the end products of bacterial fermentation of dietary fiber, and are able to regulate AMPK activity. However, it is also not clear the effect of gut microbiota-derived SCFA profile on the AMPK activity and its downstream protein expression in distinct pig breeds that are fed with the same or different fiber level. The present project aims to reveal the correlation between gut microbiota and host metabolism and possible crosstalk mechanisms via establishing animal models, such as performing fecal microbiota transplant in mice and fitting T-cannulas in the terminal ileum of pigs, and using the in vivo and in vitro approaches. The gut microbiota composition, SCFA profile，AMPK activity and the expression of its downstream proteins will be detected. Thus, the relative achievements of this study will provide evidences for further understanding interactions among nutrition, microbiota and host, interpreting the possible mechanism of gut microbiota regulating host metabolism, and illuminating the possible way manipulating pork quality by utilizing gut microbiota as the key target.

改善猪肉品质是目前养猪业面临的重大课题，宿主代谢特征是决定猪肉品质的关键因素。肠道微生物作为动物的“第二基因组”，与宿主代谢密切相关。然而，我国地方猪种与外种猪代谢特征的差异与肠道微生物关系未见报道。SCFA由肠道微生物发酵日粮纤维产生，是肠道微生物调节宿主代谢的物质基础，能调节宿主细胞代谢的关键信号分子AMPK活性。品种不同或日粮纤维水平不同情况下，肠道微生物产SCFA模式与AMPK及介导的关键蛋白表达的关系亦未见报道。本试验采用菌群移植与回肠末端造瘘技术以及体内外试验相结合的方法，研究不同品种和日粮纤维对猪肠道菌群结构和SCFA模式的影响，考察宿主AMPK及其下游关键蛋白表达规律，揭示肠道微生物与宿主代谢的关系及对话机制。研究结果为深入认识营养-微生物-宿主互作规律、阐明肠道微生物对宿主代谢调控机理及以肠道微生物为靶点调控肌肉品质提供重要理论依据。

宿主代谢特征是决定猪肉品质的关键因素。肠道微生物作为动物的“第二基因组”，与宿主代谢密切相关。本研究首先明确了脂肪型和瘦肉型猪肠道菌群结构差异及其与骨骼肌表型及糖脂代谢的关系。结果表明，与大白猪相比，荣昌猪腓肠肌MYH7、ACC、FAS、SREBP-1c与LPL表达量显著上调而MYH4与CPT-1B表达量显著下调。通过不同猪源粪菌移植于无菌小鼠发现荣昌猪和大白猪的粪便菌群结构和骨骼肌表型差异可通过菌群移植传递给无菌小鼠，并且荣昌猪粪便菌群移植可提高小鼠腓肠肌脂肪含量并促进慢肌纤维的形成。结合高纤维和低纤维饲粮补充SCFAs钠盐，揭示了SCFAs在纤维调节机体糖脂代谢中的介导作用。高纤维饲粮及添加SCFAs钠盐均能降低猪血清TG、TC和LDL-c水平，提高血清瘦素水平。同时通过回肠末端瘘管灌注和口腔灌胃的方式，系统考察了SCFAs对猪生长性能、肉品质和糖脂代谢的影响，发现不同方式外源供给SCFAs均可降低猪肝脏和背最长肌中FAS、ACC、SREBP-1c的表达量、提高CPT-1α的表达量，进而改善猪肉品质和机体糖脂代谢。体外试验进一步发现，SCFAs可通过抑制AMPK磷酸化介导其下游相关基因与蛋白表达而调节宿主糖脂代谢。此外，猪肠道微生物组成差异影响肠道发育且可通过菌群移植部分传递给无菌小鼠，而早期移植大白猪和荣昌猪粪菌不利于哺乳仔猪肠道健康。饲喂高纤维饲粮与外源供给SCFAs均可增加SCFAs产量，改善猪肠道功能。SCFAs也具有诱导抗原特异性和非特异性免疫球蛋白合成及促进T细胞增殖的功效，其机制与SCFAs受体GPR43介导有关。本研究为深入认识饲粮―肠道微生物―宿主之间的互作机制积累了资料，也为合理使用纤维和短链脂肪酸改善机体糖脂代谢和猪肉品质提供了试验依据。